On 2019-11-07 12:37:00 +0900, Junio C Hamano wrote: > Danh Doan <congdanhqx@xxxxxxxxx> writes: > > > On 2019-11-06 11:23:00 +0900, Junio C Hamano wrote: > >> > @@ -1454,7 +1454,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx) > >> > num_chunks); > >> > ctx->progress = start_delayed_progress( > >> > progress_title.buf, > >> > - num_chunks * ctx->commits.nr); > >> > + (uint64_t)num_chunks * ctx->commits.nr); > >> > >> Hmph, do we need this? I understand that the second parameter to > >> the callee is u64, so the caller needs to come up with u64 without > >> overflow, but doesn't that automatically get promoted? > > > > Neither num_chunks nor ctx->commits.nr is promoted because both of > > them are int. The result of `num_chunks * ctx->commits.nr' will be int > > and will be promoted to u64 to pass to caller. > > Ah, yes. Thanks. > > The commit title is about "integer multiplication", but can the same > issue arise with addition and subtraction as well, by the way? Yes, the same issue will arise with all binary (and ternary) arithmetic operators (+, -, *, /, %, ^, &, |, <<, >> and ?:). IIRC, gcc doesn't have any warning for this kind of issue. Microsoft Visual Studio (2017+) has C26451 for this. https://docs.microsoft.com/en-us/visualstudio/code-quality/c26451?view=vs-2017 If our friends at Microsoft could help, we can check the remaining one in our codebase. -- Danh
